\Header{correlogram}{Compute Spatial Correlograms}
\keyword{spatial}{correlogram}
\begin{Description}\relax
Compute spatial correlograms of spatial data or residuals.\end{Description}
\begin{Usage}
\begin{verbatim}
correlogram(krig, nint, plotit = TRUE,  ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{krig}] trend-surface or kriging object with columns \code{x}, \code{y}, and \code{z}

\item[\code{nint}] number of bins used

\item[\code{plotit}] logical for plotting

\item[\code{...}] parameters for the plot

\end{ldescription}
\end{Arguments}
\begin{Details}\relax
Divides range of data into \code{nint} bins, and computes the covariance for
pairs with separation in each bin, then divides by the variance.
Returns results for bins with 6 or more pairs.\end{Details}
\begin{Value}
\code{x} and \code{y} coordinates of the correlogram, and \code{cnt}, the number of pairs
averaged per bin.\end{Value}
\begin{Section}{Side Effects}
Plots the correlogram if \code{plotit = TRUE}.\end{Section}
\begin{References}\relax
Ripley, B. D. (1981) \emph{Spatial Statistics.} Wiley.

Venables, W. N. and Ripley, B. D. (2002)
\emph{Modern Applied Statistics with S.} Fourth edition.  Springer.\end{References}
\begin{SeeAlso}\relax
\code{\Link{variogram}}\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
data(topo, package="MASS")
topo.kr <- surf.ls(2, topo)
correlogram(topo.kr, 25)
d <- seq(0, 7, 0.1)
lines(d, expcov(d, 0.7))
\end{ExampleCode}
\end{Examples}

